Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

During join planning, the planner tries multiple combinations of joining
relations, thus the same base or join relation can be part of multiple of
combination. Hence remote_conds or joinclauses will get linked multiple
times as they are bidirectional lists, thus breaking linkages of previous
join combinations tried. E.g. while planning A join B join C join D planner
will come up with combinations like A(B(CD)) or (AB)(CD) or ((AB)C)D etc.
and remote_conds from A will first be linked into A(B(CD)), then AB
breaking the first linkages.

On Tue, Feb 16, 2016 at 11:36 AM, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp
> wrote:

> On 2016/02/15 21:33, Ashutosh Bapat wrote:
>
>> Here's patch with better way to fix it. I think while concatenating the
>> lists, we need to copy the lists being appended and in all the cases. If
>> we don't copy, a change in those lists can cause changes in the upward
>> linkages and thus lists of any higher level joins.
>>
>
> Maybe I'm missing something, but I don't understand why such a change in
> those lists happens. Could you explain about that in more detail?
>
> Best regards,
> Etsuro Fujita
>
>
>

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company